1. Field of the Invention
This invention relates to apparatus and methods for estimating and controlling vibration disturbances in tape drives.
2. Background of the Invention
Reliable operation of tape drive systems requires robust performance under shock and vibration conditions. Standard vibration profiles describe specifications in terms of acceleration inputs under which tape drives must operate reliably. As the track density of tape drive systems increases, which is the norm in today's environment, ensuring reliable operation under vibration conditions becomes more challenging. This is at least partly because the higher track densities reduce the amount of error that can be tolerated during read/write operations.
In tape drives, a track-follow controller is commonly used to accurately position a head actuator on the centerline of data tracks in the presence of lateral tape motion (LTM) and external disturbances like vibrations. To support the special requirements of vibration environments along with increased track density, improved track-follow performance is needed to provide reliable tape drive operation.
Currently, there are two approaches for improving track-follow performance in vibration environments. The first approach involves switching between two track-follow controllers in response to vibration changes. A low bandwidth controller is used during low vibration conditions. A high bandwidth controller is used during high vibration conditions, but is less reliable during low vibration conditions. This approach has drawbacks in that it requires reliable detection of the onset and conclusion of vibration conditions, exhibits transient behavior when switching between the controllers, and makes it difficult to evaluate stability and performance due to the hybrid control scheme.
The second approach utilizes a disturbance observer to assist a track-follow controller in the case of vibration disturbances. The disturbance observer estimates the vibration disturbance using a position measurement of the actuator and an inversion of the actuator model. This disturbance estimate is used to compensate for the disturbance effects. This approach has drawbacks in that it requires a good and stable estimate of the inverted system dynamics and does not take into account the frequency characteristics of the disturbance. A low-pass filter determines the frequency range in which a reliable estimate is provided.
In view of the foregoing, what is needed are apparatus and methods to more effectively estimate and control vibration disturbances in tape drives.